Oil recovery by in situ combustion



on. nncovnnv BY 1N srro COMBUSTION Joseph C. Trantham and Henry 0.Dixon, Bartl esville,

Okla, assignors to Phillips'Petrolenm' Company, a corporation ofDelaware No Drawing. Application May 14,1956 Serial No. 584,453

6 Claims. (ill. 166-11) This invention relates we process for therecovery of oil' by in situ combustion particularly from reservoirscontaining high gravity crude (low carbon residue) which normally burnswithout leaving a combustion-supporting residue by direct air injection.7

The recovery of oil from oil bearing formations by in situ combustion iscurrently being emphasized as a production technique. The conventionalmethod employed comprises initiating combustion of the oil adjacent abore hole in the formation by any suitable means and injecting airthrough the bore hole into the formation so as to drive the combustionzone or front radially and laterally outwardly from the bore hole. Arecent development in in situ combustion technique in the fieldof oil recoverey is disclosed and claimed in the copending' application of JohnW. Marx, Serial No. 526,388; filed August 4, 1955, now abandoned, andcomprising establishing a combustion zone around a production well byconventional methods so as" to provide a combustion Zone and a heatreservoir of sufficient extent and temperature to permit cutting thedirect flow of air through the production well and injecting air intothe formation through one or more spaced-apart wells from the productionwell so as to cause the air tofiow to the com-' bustion zone at theproduction well and support combustion therein so that the combustionfront is advanced countercurrently to the flow of air toward theinjection well or wells. This technique is designated finverse airinjection in situ combustion as opposed to direct air in-' jectionthrough the well or bore hole around which combustion is initiated.

Another recent development in recovery of oil by in situ combustion'isdisclosed in'the copending application of], C. Trantham and A.Rrschleicher, Serial No. 529,- 916, filed August 22,- 1955, andcomprises continuing the injection of air through one or more injectionwellsafter the combustion front has been'advanced, by inverse airinjection, to the injection well or wells so as to reverse the movementof the combustion front and drive the same back through the formation tothe production well around which combustion was originally initiated. Inthis technique, designated thermal echo, the returning combustion frontfeeds on the residual carbon deposited in the formation during theinverse air injection phase of the process.

It has been found that in many oil-bearing formations the crude is ofsuch high API gravity (and low carbon residue) that the hot gases from acombustion front initiated around an injection Well drive thehydrocarbon materials substantially completely away from the area infront of the combustion front thereby leaving insufficient fuel tosustain combustion and the fire goes out. This renders it impossible toinitiate combustion and build up a sufiicient combustion zone and heatreservoir to permit reversing the direction of the flow of air to thecombustion zone in order to establish inverse air injection to supportand drive the combustion zone toward the Patented .lune 9, 1959 2surrounding injection wells and away from thewell in which thecombustion is originally initiated.

Hence it is an object of the invention to provide a process or methodfor initiating in situ combustion for sup porting inverse air injectionand recovery of oil in an oil reservoir or formation containing crude ofhigh specific gravity. Another object is to provide a method of oilrecovery by in situ combustion from an oil bearing formation which isincapable of supporting in situ combustion by direct air injection;Other objects of the invention will become apparent from a considerationof the accompanying disclosure. 7

The method of the invention comprises depositing a heavy hydrocarbonoil, such as heavy crude oil', in the formation surrounding a'production well or bore hole and initiating combustion of the depositedheavy oil by any suitable conventional method so as to burn a sufiicientamount of the oil to establish a combustion zone which contains enoughheat to permit cutting off the directinjection of air or othercombustion-supporting gas and feeding air to the combustion zone fromone or more spaced-apart wells or bore holes through the formationwhereby the combustion zone is advanced toward the injection well andcombustion products and produced hydrocarbons are driven to theproduction Well from which they are recovered by conventional means. Theheavy oil is injected into the formation through a well or bore at aselected location so as to penetrate thetemperature sufficient toinitiate combustion which is in the range of approximately 500 to 700 F.

Burning of the oil in the formation surrounding the bore hole leaves acarbon residue which is sufiiciently hot to support combustion' when thedirection of the air is reversed and fed thereto from surroundinginjection wells.

The quality of depositedoil burned in the formation mu st be sufiicient'to build up a" reservoir of heat which holds the temperaturesutlicie'n'tly high to support combustion when the inverse air reachesthe combustion area. It is essential to burn only a portion of thedeposited heavy oil so that a reserve is'left to prevent vaporization ofall ofthe original oil in thefdrmation directly outside of the depositedoil and to pr'ovide'a continuous bed of fuel from the heat reservoir orcombustion zone to the injection wells. The arrival of the inverse airfrom the surrounding injection wells then revives the combustion zone.After inverse air injection and attendant combustion is established, theremaining heavy oil is burned and, as the inverse air injection iscontinued, the combustion front is propagated radially outwardly andlaterally past the limit of the heavy oil saturation and the burning iscontinued in the light oil reservoir so as to advance the combustionfront to the injection wells. In one embodiment of the invention theinjection of air is continued after arrival of the combustion front soas to reverse the direction of its movement and drive it back to theproduction well, thereby subtantially completely denuding the formationof hydrocarbons.

In order to illustrate the invention a 4 foot long stainless steel tube2 inches in diameter was filled from one end up to within 2 or 3 inchesof the other end with clean dry Wilcox sand (from the Oklahoma Cityarea). The sand was compacted in the tube and Burbank crude of highgravity and low carbon residue was forced through the sand by airpressure applied to an oil reservoir connected with the stainless steeltube by a conduit. After saturation was complete the excess crude wasblown off until a negligible amount of the crude was coming off thetube. The remaining short section of the tube was packed with ClearCreek tar sand of low gravity and high carbon residue. The packed tubewas set up in horizontal position for an in situ combustion test. Anelectrical heater was positioned at the tar sand-end of the tube and aslow stream of nitrogen was injected through the heater into the tubeduring the warm up until the sand adjacent the heater reached about 600F. at which time the nitrogen was suddenly switched ofi and air waspassed through the heater into the tar sand. lgnition of the tar wasimmediately initiated in the tar sand and after the combustion frontmoved about half the length of the tar sand section, the direction ofair was reversed so that it passed thru the sand soaked with Burbankcrude before it reached the combustion area or front and the heater wascut off. The combustion front then advanced by inverse air injectionthru the remaining tar sand and then thru the sand saturated withBurbank crude without any indication of discontinuity.

Combustion front temperatures were taken along the tube at regularintervals and it was found that the temperature ranged from 1290 to 1800F. at space velocities in the range of 350 to 420 standard cubic feetper hour/ft. (By reducing the space veiocity to the order to 250standard cubic feet per hour/ft. the temperature could probably havebeen reduced to 1050-ll50 F.)

The test demonstrates the feasibility of initiating and sustaining insitu combustion in an oil sand containing a high gravity and low carbonresidue crude by the method of the invention.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

We claim:

1. A process for recovering hydrocarbons by in situ combustion from anunderground formation containing high A.P.l. gravity crude oil ofinsufiicient carbon residue to support combustion by direct injection ofcombustion-supporting gas, comprising depositing in an area of saidformation surrounding a production borehole therein a mass of heavy oilcapable of depositing substantial combustion-supporting carbon whenburned in the formation; burning the deposited oil by direct injectionof O -containing gas thru said borehole to heat up the formationcontaining same and establish a carbon residue of sufficient temperatureto support combustion when the injection of said gas is cut off and sameis passed thru said formation to the hot coke from a surrounding area;terminating the injection of said gas thru said pro- 4 duction borehole;and injecting said gas thru said formation from a surrounding area so asto contact said hot carbon residue while at combustion-supportingtemperature to establish inverse movement of a combustion front in saidformation.

2. The process of claim 1 wherein said gas is air and inverse airinjection is effected thru a plurality of injection boreholes in saidformation spaced apart from said production borehole and combustionproducts and produced hydrocarbons are recovered from said productionborehole.

3. A process for recovering hydrocarbons by in situ combustion from anunderground formation containing high A.P.I. gravity crude oil ofsufficient carbon residue to support combustion by direct injection ofcombustion-supporting gas, comprising depositing in an area of saidformation thru at least one production borehole therein a mass of heavyoil capable of depositing combustion supporting coke when burned in theformation, said area extending into said formation several feet fromsaid borehole; burning a substantial portion but not all of thedeposited oil by air injection thru said production borehole toestablish a hot combustion zone in the form of hot carbon residue whichfunction as a heat reservoir sufiicient to maintain combustionsupporting temperatures therein while air is being passed thru at leastone injec tion borehole spaced apart from said production borehole andthru the formation to said combustion zone; when said heat reservoir isestablished, cutting off the injection of air thru said productionborehole; and then passing air to said combustion zone thru saidinjection borehole so as to advance said combustion zonecountercurrently to the flow of air.

4. The process of claim 3 wherein the injection of air is continueduntil the combustion zone has reached said at least one injectionborehole.

5. The process of claim 4 wherein the injection of air is continuedafter said combustion zone has reached said at least one injectionborehole so as to reverse the direction of said combustion zone anddrive same back toward said production well.

6. The process of claim 3 wherein combustion is initiated in a depositedmass of heavy oil adjacent a production borehole around which arepositioned several injection boreholes thru which combustion-supportingair air is injected.

References Cited in the file of this patent UNITED STATES PATENTS1,457,479 Wolcott June 5, 1923 1,978,655 Straight Oct. 30, 19342,584,606 Merriam et al. Feb. 5, 1952 2,642,943 Smith June 23, 19532,761,512 Bond Sept. 4, 1956 2,793,696 Morse May 28, 1957 AttestingOflicer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,889,881 June 9, 1959 Joseph C, Trentham at 2.1..

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should readas corrected below.

Column 1, line 29, for "recoverey" read recovery line 31., for"comprising" read comprises line 51, for "cumbustion" read m combustioncolumn 2, line 28, after "bore" insert hole -==-,3 column 4, line 14,for "sufficient" read m insufificient line 212,, for "function" readfunctions Signed and sealed this 23rd day of February 1960n SEAL) ttest:

KARL H AXLINE. ROBERT C. WATSON Commissioner of Patents

1. A PROCESS FOR RECOVERING HYDROCARBONS BY IN SITU COMBUSTION FROM ANUNDERGROUND FORMATION CONTAINING HIGH A.P.I. GRAVITY CRUDE OIL OFINSUFFICIENT CARBON RESIDUE TO SUPPORT COMBUSTION BY DIRECT INJECTION OFCOMBUSTION-SUPPORTING GAS, COMPRISING DEPOSITING IN AN AREA OF SAIDFORMATION SURROUNDING A PRODUCTION BOREHOLE THEREIN A MASS OF HEAVE OILCAPABLE OF DEPOSITING SUBSTANTIAL COMBUSTION-SUPPORTING CARBON WHENBURNED IN THE FORMATION; BURNING THE DEPOSITED OIL BY DIRECT INJECTIONOF O2-CONTAINING GAS THRU SAID BOREHOLE TO HEAT UP THE FORMATIONCONTAINING SAME AND ESTABLISH A CARBON RESIDUE OF SUFFICIENT TEMPERATURETO SUPPORT COMBUSTION, WHEN THE INJECTION OF SAID GAS IS CUT OFF ANDSAME IS PASSED THRU SAID FORMATION TO THE HOT COKE FROM THE SURROUNDINGAREA; TERMINATING THE INJECTION OF SAID GAS THRU SAID PRODUCTIONBOREHOLE; AND INJECTING SAID GAS THRU SAID FORMATION FROM A SURROUNDINGAREA SO AS TO CONTACT SAID HOT CARBON RESIDUE WHILE ATCOMBUSTION-SUPPORTING TEMPERATURE TO ESTABLISH INVERSE MOVEMENT OF ACOMBUSTION FRONT IN SAID FORMATION.